High-speed RFID tag assembly using impulse heating

ABSTRACT

RFID inlays or straps may be assembled using impulse heating of metal precursors. Metal precursors are applied to and/or included in contacts on an RFID IC and/or terminals on a substrate. During assembly of the tag, the IC is disposed onto the substrate such that the IC contacts physically contact either the substrate terminals or metal precursors that in turn physically contact the substrate terminals. Impulse heating is then used to rapidly apply heat to the metal precursors, processing them into metallic structures that electrically couple the IC contacts to the substrate terminals.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation under 35 U.S.C. § 120 of co-pendingU.S. patent application Ser. No. 17/101,085 filed on Nov. 23, 2020,which is a continuation under 35 U.S.C. § 120 of co-pending U.S. patentapplication Ser. No. 15/789,339 filed on Oct. 20, 2017, which is acontinuation under 35 U.S.C. § 120 of U.S. patent application Ser. No.14/327,207 filed on Jul. 9, 2014, now U.S. Pat. No. 9,846,833 issued inDec. 19, 2017, which is a continuation-in-part of U.S. patentapplication Ser. No. 13/776,346 filed on Feb. 25, 2013, now U.S. Pat.No. 8,881,373 issued in Nov. 11, 2014, which is a continuation-in-partof U.S. patent application Ser. No. 13/456,653 filed on Apr. 26, 2012,now U.S. Pat. No. 8,661,562 issued in Mar. 4, 2014, which is adivisional of U.S. patent application Ser. No. 12/399,913 filed on Mar.6, 2009, now U.S. Pat. No. 8,188,927 issued in May 29, 2012, whichclaims benefit of U.S. Provisional Application Ser. No. 61/035,710 filedon Mar. 11, 2008. The U.S. patent application Ser. No. 13/776,346 alsoclaims benefit of U.S. Provisional Application Ser. No. 61/713,058 filedon Oct. 12, 2012. The U.S. Patent Application Ser. No. 14/327,207 alsoclaims the benefit of U.S. Provisional Patent Application Ser. No.61/844,826 filed on Jul. 10, 2013. The disclosures of the above patentapplications are hereby incorporated by reference for all purposes.

BACKGROUND

Radio-Frequency Identification (RFID) systems typically include RFIDreaders, also known as RFID reader/writers or RFID interrogators, andRFID tags. RFID systems can be used in many ways for locating andidentifying objects to which the tags are attached. RFID systems areuseful in product-related and service-related industries for trackingobjects being processed, inventoried, or handled. In such cases, an RFIDtag is usually attached to an individual item, or to its package.

In principle, RFID techniques entail using an RFID reader to interrogateone or more RFID tags. The reader transmitting a Radio Frequency (RF)wave performs the interrogation. The RF wave is typicallyelectromagnetic, at least in the far field. The RF wave can also bepredominantly electric or magnetic in the near field. The RF wave mayencode one or more commands that instruct the tags to perform one ormore actions.

A tag that senses the interrogating RF wave may respond by transmittingback another RF wave. The tag either generates the transmitted back RFwave originally, or by reflecting back a portion of the interrogating RFwave in a process known as backscatter. Backscatter may take place in anumber of ways.

The reflected-back RF wave may encode data stored in the tag, such as anumber. The response is demodulated and decoded by the reader, whichthereby identifies, counts, or otherwise interacts with the associateditem. The decoded data can denote a serial number, a price, a date, adestination, other attribute(s), any combination of attributes, and soon. Accordingly, when a reader receives tag data it can learn about theitem that hosts the tag and/or about the tag itself.

An RFID tag typically includes an antenna section, a radio section, apower-management section, and frequently a logical section, a memory, orboth. In some RFID tags the power-management section included an energystorage device such as a battery. RFID tags with an energy storagedevice are known as battery-assisted, semi-active, or active tags. OtherRFID tags can be powered solely by the RF signal they receive. Such RFIDtags do not include an energy storage device and are called passivetags. Of course, even passive tags typically include temporary energy-and data/flag-storage elements such as capacitors or inductors.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

Embodiments are directed to assembling RFID inlays or straps usingimpulse heating of metal precursors. Metal precursors are applied toand/or included in contacts on an RFID IC and/or terminals on asubstrate. During assembly of the tag, the IC is disposed onto thesubstrate such that the IC contacts physically contact either thesubstrate terminals or metal precursors that in turn physically contactthe substrate terminals. Impulse heating is then used to rapidly applyheat to the metal precursors, processing them into metallic structuresthat electrically couple the IC contacts to the substrate terminals.

These and other features and advantages will be apparent from a readingof the following detailed description and a review of the associateddrawings. It is to be understood that both the foregoing generaldescription and the following detailed description are explanatory onlyand are not restrictive of aspects as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description proceeds with reference to theaccompanying Drawings, in which:

FIG. 1 is a block diagram of components of an RFID system.

FIG. 2 is a diagram showing components of a passive RFID tag, such as atag that can be used in the system of FIG. 1 .

FIG. 3 is a conceptual diagram for explaining a half-duplex mode ofcommunication between the components of the RFID system of FIG. 1 .

FIG. 4 is a block diagram showing a detail of an RFID tag, such as theone shown in FIG. 2 .

FIG. 5A and 5B illustrate signal paths during tag-to-reader andreader-to-tag communications in the block diagram of FIG. 4 .

FIG. 6 illustrates tag antenna mounting with a repassivation layer toreduce variations in mounting capacitance between an IC and a tagantenna layer according to embodiments.

FIG. 7 illustrates a detailed cross-section of a conductiveredistribution layer electrically coupling to an IC contact according toembodiments.

FIG. 8 depicts patterned contact pads according to embodiments.

FIG. 9 depicts nonoverlapping or offset contacts according toembodiments.

FIG. 10 illustrates a tag assembly method according to embodiments.

FIGS. 11A and 11B illustrate tag precursors having ICs galvanicallyconnected to antenna terminals on tag substrates according toembodiments.

FIG. 12 depicts the deposition of metal precursors on RFID integratedcircuits according to embodiments.

FIG. 13 depicts the assembly of RFID ICs to form tags or straps usingimpulse heating of metal precursors according to embodiments.

FIG. 14 is a flowchart depicting a process for assembling RFID ICs toform tags or straps using impulse heating of metal precursors accordingto embodiments.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments or examples. These embodimentsor examples may be combined, other aspects may be utilized, andstructural changes may be made without departing from the spirit orscope of the present disclosure. The following detailed description istherefore not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

As used herein, “memory” is one of ROM, RAM, SRAM, DRAM, NVM, EEPROM,FLASH, Fuse, MRAM, FRAM, and other similar information-storagetechnologies as will be known to those skilled in the art. Some portionsof memory may be writeable and some not. “Command” refers to a readerrequest for one or more tags to perform one or more actions, andincludes one or more tag instructions preceded by a command identifieror command code that identifies the command and/or the tag instructions.“Instruction” refers to a request to a tag to perform a single explicitaction (e.g., write data into memory). “Program” refers to a request toa tag to perform a set or sequence of instructions (e.g., read a valuefrom memory and, if the read value is less than a threshold then lock amemory word). “Protocol” refers to an industry standard forcommunications between a reader and a tag (and vice versa), such as theClass-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960MHz by GS1 EPCglobal, Inc. (“Gen2 Specification”), versions 1.2.0 and2.0 of which are hereby incorporated by reference.

FIG. 1 is a diagram of the components of a typical RFID system 100,incorporating embodiments. An RFID reader 110 transmits an interrogatingRF signal 112. RFID tag 120 in the vicinity of RFID reader 110 sensesinterrogating RF signal 112 and generate signal 126 in response. RFIDreader 110 senses and interprets signal 126. The signals 112 and 126 mayinclude RF waves and/or non-propagating RF signals (e.g., reactivenear-field signals).

Reader 110 and tag 120 communicate via signals 112 and 126. Whencommunicating, each encodes, modulates, and transmits data to the other,and each receives, demodulates, and decodes data from the other. Thedata can be modulated onto, and demodulated from, RF waveforms. The RFwaveforms are typically in a suitable range of frequencies, such asthose near 900 MHz, 13.56 MHz, and so on.

The communication between reader and tag uses symbols, also called RFIDsymbols. A symbol can be a delimiter, a calibration value, and so on.Symbols can be implemented for exchanging binary data, such as “0” and“1”, if that is desired. When symbols are processed by reader 110 andtag 120 they can be treated as values, numbers, and so on.

Tag 120 can be a passive tag, or an active or battery-assisted tag(i.e., a tag having its own power source). When tag 120 is a passivetag, it is powered from signal 112.

FIG. 2 is a diagram of an RFID tag 220, which may function as tag 120 ofFIG. 1 . Tag 220 is drawn as a passive tag, meaning it does not have itsown power source. Much of what is described in this document, however,applies also to active and battery-assisted tags.

Tag 220 is typically (although not necessarily) formed on asubstantially planar inlay 222, which can be made in many ways known inthe art. Tag 220 includes a circuit which may be implemented as an IC224. In some embodiments IC 224 is implemented in complementarymetal-oxide semiconductor (CMOS) technology. In other embodiments IC 224may be implemented in other technologies such as bipolar junctiontransistor (BJT) technology, metal-semiconductor field-effect transistor(MESFET) technology, and others as will be well known to those skilledin the art. IC 224 is arranged on inlay 222.

Tag 220 also includes an antenna for exchanging wireless signals withits environment. The antenna is often flat and attached to inlay 222. IC224 is electrically coupled to the antenna via suitable IC contacts (notshown in FIG. 2 ). The term “electrically coupled” as used herein maymean a direct electrical connection, or it may mean a connection thatincludes one or more intervening circuit blocks, elements, or devices.The “electrical” part of the term “electrically coupled” as used in thisdocument shall mean a coupling that is one or more of ohmic/galvanic,capacitive, and/or inductive. Similarly, the term “electricallyisolated” as used herein means that electrical coupling of one or moretypes (e.g., galvanic, capacitive, and/or inductive) is not present, atleast to the extent possible. For example, elements that areelectrically isolated from each other are galvanically isolated fromeach other, capacitively isolated from each other, and/or inductivelyisolated from each other. Of course, electrically isolated componentswill generally have some unavoidable stray capacitive or inductivecoupling between them, but the intent of the isolation is to minimizethis stray coupling to a negligible level when compared with anelectrically coupled path.

IC 224 is shown with a single antenna port, comprising two IC contactselectrically coupled to two antenna segments 226 and 228 which are shownhere forming a dipole. Many other embodiments are possible using anynumber of ports, contacts, antennas, and/or antenna segments.

Diagram 250 depicts top and side views of tag 252, formed using a strap.Tag 252 differs from tag 220 in that it includes a substantially planarstrap substrate 254 having strap contacts 256 and 258. IC 224 is mountedon strap substrate 254 such that the IC contacts on IC 224 electricallycouple to strap contacts 256 and 258 via suitable connections (notshown). Strap substrate 254 is then placed on inlay 222 such that strapcontacts 256 and 258 electrically couple to antenna segments 226 and228. Strap substrate 254 may be affixed to inlay 222 via pressing, aninterface layer, one or more adhesives, or any other suitable means.

Diagram 260 depicts a side view of an alternative way to place strapsubstrate 254 onto inlay 222. Instead of strap substrate 254's surface,including strap contacts 256/258, facing the surface of inlay 222, strapsubstrate 254 is placed with its strap contacts 256/258 facing away fromthe surface of inlay 222. Strap contacts 256/258 can then be eithercapacitively coupled to antenna segments 226/228 through strap substrate254, or conductively coupled using a through-via which may be formed bycrimping strap contacts 256/258 to antenna segments 226/228. In someembodiments the positions of strap substrate 254 and inlay 222 may bereversed, with strap substrate 254 mounted beneath strap substrate 222and strap contacts 256/258 electrically coupled to antenna segments226/228 through inlay 222. Of course, in yet other embodiments strapcontacts 256/258 may electrically couple to antenna segments 226/228through both inlay 222 and strap substrate 254.

In operation, the antenna receives a signal and communicates it to IC224, which both harvests power and responds if appropriate, based on theincoming signal and the IC's internal state. If IC 224 uses backscattermodulation then it responds by modulating the antenna's reflectance,which generates response signal 126 from signal 112 transmitted by thereader. Electrically coupling and uncoupling the IC contacts of IC 224can modulate the antenna's reflectance, as can varying the admittance ofa shunt-connected circuit element which is coupled to the IC contacts.Varying the impedance of a series-connected circuit element is anothermeans of modulating the antenna's reflectance.

In the embodiments of FIG. 2 , antenna segments 226 and 228 are separatefrom IC 224. In other embodiments the antenna segments may alternativelybe formed on IC 224. Tag antennas according to embodiments may bedesigned in any form and are not limited to dipoles. For example, thetag antenna may be a patch, a slot, a loop, a coil, a horn, a spiral, amonopole, microstrip, stripline, or any other suitable antenna.

The components of the RFID system of FIG. 1 may communicate with eachother in any number of modes. One such mode is called full duplex.Another such mode is called half-duplex, and is described below.

FIG. 3 is a conceptual diagram 300 for explaining half-duplexcommunications between the components of the RFID system of FIG. 1 , inthis case with tag 120 implemented as passive tag 220 of FIG. 2 . Theexplanation is made with reference to a TIME axis, and also to a humanmetaphor of “talking” and “listening”. The actual technicalimplementations for “talking” and “listening” are now described.

RFID reader 110 and RFID tag 120 talk and listen to each other by takingturns. As seen on axis TIME, when reader 110 talks to tag 120 thecommunication session is designated as “R→T”, and when tag 120 talks toreader 110 the communication session is designated as “T→R”. Along theTIME axis, a sample R→T communication session occurs during a timeinterval 312, and a following sample T→R communication session occursduring a time interval 326. Of course interval 312 is typically of adifferent duration than interval 326—here the durations are shownapproximately equal only for purposes of illustration.

According to blocks 332 and 336, RFID reader 110 talks during interval312, and listens during interval 326. According to blocks 342 and 346,RFID tag 120 listens while reader 110 talks (during interval 312), andtalks while reader 110 listens (during interval 326).

In terms of actual behavior, during interval 312 reader 110 talks to tag120 as follows. According to block 352, reader 110 transmits signal 112,which was first described in FIG. 1 . At the same time, according toblock 362, tag 120 receives signal 112 and processes it to extract dataand so on. Meanwhile, according to block 372, tag 120 does notbackscatter with its antenna, and according to block 382, reader 110 hasno signal to receive from tag 120.

During interval 326, tag 120 talks to reader 110 as follows. Accordingto block 356, reader 110 transmits a Continuous Wave (CW) signal, whichcan be thought of as a carrier that typically encodes no information.This CW signal serves both to transfer energy to tag 120 for its owninternal power needs, and also as a carrier that tag 120 can modulatewith its backscatter. Indeed, during interval 326, according to block366, tag 120 does not receive a signal for processing. Instead,according to block 376, tag 120 modulates the CW emitted according toblock 356 so as to generate backscatter signal 126. Concurrently,according to block 386, reader 110 receives backscatter signal 126 andprocesses it.

FIG. 4 is a block diagram showing a detail of an RFID IC, such as IC 224in FIG. 2 . Electrical circuit 424 in FIG. 4 may be formed in an IC ofan RFID tag, such as tag 220 of FIG. 2 . Circuit 424 has a number ofmain components that are described in this document. Circuit 424 mayhave a number of additional components from what is shown and described,or different components, depending on the exact implementation.

Circuit 424 shows two IC contacts 432, 433, suitable for coupling toantenna segments such as antenna segments 226/228 of RFID tag 220 ofFIG. 2 . When two IC contacts form the signal input from and signalreturn to an antenna they are often referred-to as an antenna port. ICcontacts 432, 433 may be made in any suitable way, such as from metallicpads and so on. In some embodiments circuit 424 uses more than two ICcontacts, especially when tag 220 has more than one antenna port and/ormore than one antenna.

Circuit 424 includes signal-routing section 435 which may include signalwiring, signal-routing busses, receive/transmit switches, and so on thatcan route a signal to the components of circuit 424. In some embodimentsIC contacts 432/433 couple galvanically and/or inductively tosignal-routing section 435. In other embodiments (such as is shown inFIG. 4 ) circuit 424 includes optional capacitors 436 and/or 438 which,if present, capacitively couple IC contacts 432/433 to signal-routingsection 435. This capacitive coupling causes IC contacts 432/433 to begalvanically decoupled from signal-routing section 435 and other circuitcomponents.

Capacitive coupling (and resultant galvanic decoupling) between ICcontacts 432 and/or 433 and components of circuit 424 is desirable incertain situations. For example, in some RFID tag embodiments ICcontacts 432 and 433 may galvanically connect to terminals of a tuningloop on the tag. In this situation, capacitors 436 and/or 438galvanically decouple IC contact 432 from IC contact 433, therebypreventing the formation of a short circuit between the IC contactsthrough the tuning loop.

Capacitors 436/438 may be implemented within circuit 424 and/or partlyor completely external to circuit 424. For example, a dielectric orinsulating layer on the surface of the IC containing circuit 424 mayserve as the dielectric in capacitor 436 and/or capacitor 438. Asanother example, a dielectric or insulating layer on the surface of atag substrate (e.g., inlay 222 or strap substrate 254) may serve as thedielectric in capacitors 436/438. Metallic or conductive layerspositioned on both sides of the dielectric layer (i.e., between thedielectric layer and the IC and between the dielectric layer and the tagsubstrate) may then serve as terminals of the capacitors 436/438. Theconductive layers may include IC contacts (e.g., IC contacts 432/433),antenna segments (e.g., antenna segments 226/228), or any other suitableconductive layers.

Circuit 424 also includes a rectifier and PMU (Power Management Unit)441 that harvests energy from the RF signal received by antenna segments226/228 to power the circuits of IC 424 during either or bothreader-to-tag (R→T) and tag-to-reader (T→R) sessions. Rectifier and PMU441 may be implemented in any way known in the art.

Circuit 424 additionally includes a demodulator 442 that demodulates theRF signal received via IC contacts 432, 433. Demodulator 442 may beimplemented in any way known in the art, for example including a slicer,an amplifier, and so on.

Circuit 424 further includes a processing block 444 that receives theoutput from demodulator 442 and performs operations such as commanddecoding, memory interfacing, and so on. In addition, processing block444 may generate an output signal for transmission. Processing block 444may be implemented in any way known in the art, for example bycombinations of one or more of a processor, memory, decoder, encoder,and so on.

Circuit 424 additionally includes a modulator 446 that modulates anoutput signal generated by processing block 444. The modulated signal istransmitted by driving IC contacts 432, 433, and therefore driving theload presented by the coupled antenna segment or segments. Modulator 446may be implemented in any way known in the art, for example including aswitch, driver, amplifier, and so on.

In one embodiment, demodulator 442 and modulator 446 may be combined ina single transceiver circuit. In another embodiment modulator 446 maymodulate a signal using backscatter. In another embodiment modulator 446may include an active transmitter. In yet other embodiments demodulator442 and modulator 446 may be part of processing block 444.

Circuit 424 additionally includes a memory 450 to store data 452. Atleast a portion of memory 450 is preferably implemented as a NonvolatileMemory (NVM), which means that data 452 is retained even when circuit424 does not have power, as is frequently the case for a passive RFIDtag.

In some embodiments, particularly in those with more than one antennaport, circuit 424 may contain multiple demodulators, rectifiers, PMUs,modulators, processing blocks, and/or memories.

In terms of processing a signal, circuit 424 operates differently duringa R→T session and a T→R session. The different operations are describedbelow, in this case with circuit 424 representing an IC of an RFID tag.

FIG. 5A shows version 524-A of components of circuit 424 of FIG. 4 ,further modified to emphasize a signal operation during a R→T sessionduring time interval 312 of FIG. 3 . Demodulator 442 demodulates an RFsignal received from IC contacts 432, 433. The demodulated signal isprovided to processing block 444 as C_IN. In one embodiment, C_IN mayinclude a received stream of symbols.

Version 524-A shows as relatively obscured those components that do notplay a part in processing a signal during a R→T session. Rectifier andPMU 441 may be active, such as for converting RF power. Modulator 446generally does not transmit during a R→T session, and typically does notinteract with the received RF signal significantly, either becauseswitching action in section 435 of FIG. 4 decouples modulator 446 fromthe RF signal, or by designing modulator 446 to have a suitableimpedance, and so on.

Although modulator 446 is typically inactive during a R→T session, itneed not be so. For example, during a R→T session modulator 446 could beadjusting its own parameters for operation in a future session, and soon.

FIG. 5B shows version 524-B of components of circuit 424 of FIG. 4 ,further modified to emphasize a signal operation during a T→R sessionduring time interval 326 of FIG. 3 . Processing block 444 outputs asignal C_OUT. In one embodiment, C_OUT may include a stream of symbolsfor transmission. Modulator 446 then modulates C_OUT and provides it toantenna segments such as segments 226/228 of RFID tag 220 via ICcontacts 432, 433.

Version 524-B shows as relatively obscured those components that do notplay a part in processing a signal during a T→R session. Rectifier andPMU 441 may be active, such as for converting RF power. Demodulator 442generally does not receive during a T→R session, and typically does notinteract with the transmitted RF signal significantly, either becauseswitching action in section 435 of FIG. 4 decouples demodulator 442 fromthe RF signal, or by designing demodulator 442 to have a suitableimpedance, and so on.

Although demodulator 442 is typically inactive during a T→R session, itneed not be so. For example, during a T→R session demodulator 442 couldbe adjusting its own parameters for operation in a future session, andso on.

In typical embodiments, demodulator 442 and modulator 446 are operableto demodulate and modulate signals according to a protocol, such as theGen2 Specification mentioned above. In embodiments where circuit 424includes multiple demodulators and/or modulators, each may be configuredto support different protocols or different sets of protocols. Aprotocol specifies, in part, symbol encodings, and may include a set ofmodulations, rates, timings, or any other parameter associated with datacommunications. In addition, a protocol can be a variant of a statedspecification such as the Gen2 Specification, for example includingfewer or additional commands than the stated specification calls for,and so on. In such instances, additional commands are sometimes calledcustom commands.

An RFID tag may be manufactured by physically attaching an RFID IC to atag inlay having a substrate and an antenna, and electrically couplingthe RFID IC to the antenna. For example, the RFID IC may be pressed ontothe tag inlay and then electrically coupled to the antenna via one ormore contact bumps on the IC and/or on the antenna. However, onechallenge with this manufacturing method is that the mounting force forpressing the IC and the tag inlay together may vary from tag to tag, inturn affecting the electrical properties and performance of thecompleted tag. An RFID IC and its coupled antenna form a tuned circuitwhose tuning varies, in part, with the amount of unwanted parasiticcapacitive coupling between circuits in the IC and the antenna. Thisparasitic mounting capacitance can be quantified as:

$\begin{matrix}{C = {\varepsilon_{0}\varepsilon_{r}\frac{A}{d}}} & \lbrack 1\rbrack\end{matrix}$where ε₀ is the free-space permittivity, ε_(r) is the relativepermittivity, A is the area of the overlap between the antenna and thecircuits, and d is the distance between the antenna and the circuits.Ideally, the area A varies by only a small amount, both because an RFIDIC can typically be placed onto the inlay with good placement accuracy,and because the overlap is approximately constant even if the IC is notplaced accurately because this capacitance is distributed over theentire area of the IC-to-antenna overlap. The distance d, however canchange significantly with the mounting force applied during the mountingprocess, causing correspondingly significant changes in capacitance C.Hence, variations in mounting force result in tags with varying mountingcapacitances and therefore varying tuning.

In embodiments, a nonconductive repassivation layer may be used toreduce variations in mounting capacitance. The repassivation layer maycover a surface of the IC, be disposed between the IC and a substrate,or be disposed between IC contact pads and the rest of the IC. In someembodiments the repassivation layer mitigates mounting-capacitancevariations by ensuring a fixed distance between the circuits of the ICand the antenna layer. In other embodiments the repassivation layermitigates parasitic capacitance variations between circuits of the ICand large IC contact pads, again by ensuring a fixed distance betweenthese circuits and the contact pads.

FIG. 6 illustrates IC-to-tag antenna mounting with a repassivation layerto reduce mounting-capacitance variations.

FIG. 6 shows a diagram 600 in which an RFID strap or inlay comprisingsubstrate 622 and antenna terminals 626 is pressed against RFID IC 624with a mounting force F1 (602), where antenna terminals 626 areseparated from IC 624 by at least a repassivation layer 630. Mountingdistance D1 (604) is fixed by repassivation layer 630, producing asimilarly fixed mounting capacitance C1.

Diagram 650 shows the RFID strap or inlay being pressed against the RFIDIC with a mounting force F2 (652) which is larger than mounting force F1(602). The repassivation layer 630 ensures that mounting distance D2(654) is substantially the same as mounting distance D1 (604) despitethe larger mounting force F2. As a result, mounting capacitance C2 issubstantially similar to mounting capacitance C1, helping ensure thatthe tags have similar tuning and consequent similar performance.

In some embodiments a conductive redistribution layer 634 covers a largeportion of the surface of either RFID IC 624 or repassivation layer 630.Conductive redistribution layer 634 may be metal (e.g., copper,aluminum, gold, palladium, or any other suitable metal), doped silicon,graphene, or another material that is electrically conductive orpossesses metallic properties. Conductive redistribution layer 634 maybe applied or deposited on repassivation layer 630, for example byevaporation, sputtering, or direct transfer.

Repassivation layer 630 and/or conductive redistribution layer 634 maybe confined within at least a portion of a surface of IC 624. Forexample, repassivation layer 630 may be confined within the perimeter ofIC 624, and redistribution layer 634 may be confined within theperimeter of repassivation layer 630. In other embodiments,repassivation layer 630 and/or redistribution layer 634 may extendbeyond the perimeter of IC 624. For example, at least a portion ofrepassivation layer 630 may extend beyond the perimeter of IC 624, or atleast a portion of redistribution layer 634 may extend beyond theperimeter of repassivation layer 630. In some embodiments, the portionsof repassivation layer 630/redistribution layer 634 that extend beyond aperimeter of the underlying surface (e.g., that of IC 624 orrepassivation layer 630) may be removed by stripping, etching, or as aby-product of singulating IC 624. In other embodiments, the extendedportions of repassivation layer 630/redistribution layer 634 may wraparound or encroach onto one or more neighboring surfaces of the IC, ormay extend out from the IC surface in a cantilevered fashion.

Repassivation layer 630 and/or conductive redistribution layer 634 mayalso be deposited or processed to have a particular pattern. Forexample, repassivation layer 630 may have a pattern of any desired shapethat uncovers all or a portion of IC contacts 633, uncovers otherportions of the surface of IC 624, and/or covers an entire surface of IC624. Similarly, redistribution layer 634 may be patterned to formcontact pads, strips, or any other desired shape, and may cover all or aportion of IC contacts 633. The patterning of repassivation layer 630and/or redistribution layer 634 may be performed using a masking step todefine the desired pattern (e.g., with a masking layer) and an etchingstep (if masking occurs after layer deposition) or a liftoff/removalstep (if masking occurs before layer deposition). In some embodiments,repassivation layer 630 and/or redistribution layer 634 may be appliedto another substrate, optionally patterned, and then transferred to IC624.

In some embodiments, repassivation layer 630 may include an air gap thatseparates conductive redistribution layer 634 from IC 624 to furtherdecouple the two capacitively. The air gap may be bridged by supportpillar(s) between conductive redistribution layer 634 and IC 624(including contacts that electrically couple the two). In someembodiments, conductive redistribution layer 634 may employ a metallicor conductive mesh structure to further reduce the capacitive coupling.

Conductive redistribution layer 634 may comprise a single or multipleportions. For example, conductive redistribution layer 634 onrepassivation layer 630 may be patterned to provide multiple contactareas electrically isolated from each other. In some embodiments,conductive redistribution layer 634 may also help to protect theunderlying repassivation layer 630 during IC fabrication. For example,conductive redistribution layer 634 may serve as an etch mask thatcovers and prevents etching or damage to underlying portions ofrepassivation layer 634 during processing like that described in U.S.Pat. No. 7,482,251 issued on Jan. 27, 2009, the entirety of which ishereby incorporated by reference.

As described above, repassivation layer 630 may have a pattern thatuncovers at least a portion of IC contacts 633. For example,repassivation layer 630 may be patterned to leave openings over at leasta portion of IC contacts 633, or may be patterned such that at least aportion of IC contacts 633 lie outside the periphery of repassivationlayer 630. By contrast, redistribution layer 634 may have a pattern thatcovers at least a portion of IC contacts 633. In some embodiments, afirst pattern of repassivation layer 630 and a second pattern ofredistribution layer 634 may be chosen such that the portions of ICcontacts 633 uncovered by the first pattern at least partially coincidewith the portions of IC contacts 633 that are covered by the secondpattern.

Redistribution layer 634 may be galvanically (i.e., conductively)connected to the portion(s) of IC contacts 633 uncovered by the firstpattern and covered by the second pattern. In some embodiments, thesecond pattern may be deposited directly over portions of IC contacts633 uncovered by the first pattern and processed to form galvanicconnections to IC contacts 633 without the need for bumps or otherintermediaries. For example, redistribution layer 634 may be depositedover openings in repassivation layer 630 that uncover portions of ICcontacts 633, or may be deposited to extend beyond the periphery ofrepassivation layer 630 if portions of IC contacts 633 lie outside theperiphery of repassivation layer 630. This latter embodiment isdescribed in more detail below in FIG. 7 . In other embodiments one ormore bumps 632 may galvanically connect redistribution layer 634 and ICcontacts 633.

In some embodiments, IC contacts 633 may be electrically coupled toredistribution layer 634 without uncovering portions of IC contacts 633.For example, portions of repassivation layer 630 may be made conductive,for example by doping via ion implantation, allowing IC contacts 633 togalvanically connect with redistribution layer 634 through theseconductive portions. In another example, IC contacts 633 maycapacitively couple to conductive redistribution layer 634 throughrepassivation layer 630. For example, repassivation layer 630 may serveas a capacitor dielectric between IC contacts 633 and conductiveredistribution layer 634. In cases where multiple, separate portions ofconductive redistribution layer 634 exist, multiple capacitors may beformed between the separate portions of conductive redistribution layer634 and corresponding IC contacts, where each distinct capacitor may becoupled to distinct electrical circuits of the IC such as a rectifiercircuit, a demodulator circuit, or a modulator circuit, thus enablingthese circuits to be at different DC potentials. According to otherembodiments, another antenna terminal may be affixed to a second surfaceof the IC (opposite the first surface) forming another capacitor (or setof capacitors) on the surface of the chip. In cases with multiplecapacitors (and/or two-sided coupling), one or more connections mayinstead be galvanic by providing a direct contact between the antennatrace and one or more large contact pads on the IC.

Repassivation layer 630 may be an organic or inorganic material,typically (although not necessarily) with a relatively low dielectricconstant and a reasonable thickness to minimize parasitic couplingcapacitance as described above. Examples of organic materials includebut are not limited to polyimide-based materials, Spheron™ WLPmanufactured by RoseStreet Labs based in Phoenix, AZ, orbenzocyclobutene-based materials (e.g., bisbenzocyclobutene, BCB). Anadditional layer 636 may be applied between the IC and the strap/inlayto attach the IC to the strap/inlay, physically and/or electrically.Layer 636 may include an anisotropic conductive adhesive or layer, apatterned conductive adhesive or layer, and/or a nonconductive adhesiveor layer. If layer 636 is nonconductive then it is typicallysufficiently thin as to provide low-impedance capacitive couplingbetween antenna terminals 626 and conductive redistribution layer 634 atthe frequencies of RFID communications. Whereas FIG. 6 shows layer 636contacting both of the terminals of antenna 626 and both portions ofconductive redistribution layer 634, in some embodiments layer 636 maybe patterned to prevent antenna terminals 626 from coupling with eachother, or to prevent portions of conductive redistribution layer 634from coupling with each other. For example, layer 636 may be patternedsuch that a portion of conductive redistribution layer 634 onlygalvanically couples with one of the antenna terminals, and does notgalvanically couple with the other antenna terminal or with otherportions of conductive redistribution layer 634. Of course, in someembodiments layer 636 may not be present at all.

FIG. 7 illustrates a cross-section 700 of conductive redistributionlayer 634 electrically coupling to IC contact 633 according toembodiments. As shown in cross-section 700, repassivation layer 630 isdisposed on RFID IC 624 so as to at least partially cover one of itssurfaces, leaving other portions of the surface uncovered. In FIG. 7 asshown, repassivation layer 630 optionally leaves uncovered a portion ofIC contact 633. Also in FIG. 7 as shown, in some embodiments at leastpart of an edge of repassivation layer 630 may be sloped or beveled.Conductive redistribution layer 634 may be disposed on IC 624 so as toextend from the top of repassivation layer 630 down its sloped/beveledside, forming what may be referred to as a “side contact”. Side contact710 may further extend beyond the periphery of repassivation layer 630and over at least a portion of IC contact 633, coupling galvanically orcapacitively to a portion of IC contact 633. In some embodiments theextension of side contact 710 may couple to IC contact 633 directly,without intermediate contacts, bumps, or layers. In other embodimentsone or more conductive and/or nonconductive contacts, bumps or layersmay be interposed between the extension of side contact 710 and ICcontact 633.

Conductive redistribution layer 634 also electrically couples to antenna624 directly or through an optional conductive/nonconductive layer oradhesive 636, as described above. In some embodiments, in particularthose similar to diagram 700, the region of electrical coupling betweenconductive redistribution layer 634 and antenna 624 substantiallynonoverlaps the region of electrical coupling between conductiveredistribution layer 634 and IC contact 633. In other words, theprojection of the electrical interface area between conductiveredistribution layer 634 and antenna 624 onto the surface of the IC 624does not overlap the projection of the electrical interface area betweenconductive redistribution layer 634 and IC contact 633.

As described above, in many cases RFID ICs can be placed onto an inlaywith relatively good placement accuracy. Accurate alignment of an IC toan inlay antenna allows proper coupling between the IC contacts and theantenna terminals. One way to couple the IC to the antenna terminalsinvolves using metallic posts, also known as bumps. However, in somesituations using bumps for coupling may be undesirable. Bumps form astress point on the IC, reducing its strength and potentially resultingin IC breakage during further processing.

In embodiments according to the present invention, one or morerelatively large conductive contact pads formed on the IC may be usedinstead of (or in addition to) bumps. Diagram 800 in FIG. 8 depicts atop view of IC 802 having large contact pads 808 and 810. In diagram 800each large contact pad is electrically coupled to IC 802 via a pair ofIC contacts, but more or fewer IC contacts can be used. In someembodiments the large contract pads 808 and 810 are galvanically coupledto the IC contacts, whereas in other embodiments the coupling may becapacitive or inductive.

As depicted in diagram 800, large contact pad 808 is electricallycoupled to IC 802 via IC contacts 804 a and 804 b, and large contact pad810 is electrically coupled to IC 802 via IC contacts 806 a and 806 b.Large contact pads 808 and 810 are, in turn, configured to providecapacitive or galvanic coupling to external electrical elements such asthe antenna terminals on an RFID strap or inlay (e.g., antenna terminals626). Large contact pads 808 and 810 provide more area for coupling tothese external electrical elements, and as a result reduce the couplingimpedance. They also reduce performance variations due to IC-to-antennaalignment accuracy because the predominant parasitic capacitive couplingis IC-to-contact pad rather than IC-to-antenna, and theIC-to-contact-pad alignment is typically very well controlled becausethe large contact pads are fabricated on IC 802.

In some embodiments, a dielectric or repassivation layer (e.g.,repassivation layer 630) is first deposited on IC 802, and large contactpads 808/810 are formed on the repassivation layer and then electricallycoupled to the IC contacts. The coupling between the large contact padsand the IC contacts may be capacitive or galvanic. When capacitive, thecoupling may be adjusted via the dielectric characteristics (e.g.composition, thickness) of the material disposed between the contactpads and the antenna (e.g., layer 636). This material may benonconductive material covering the pads, nonconductive materialcovering the antenna traces (e.g. a naturally grown or enhanced oxidelayer on aluminum traces), and/or any additional dielectric material.Galvanic coupling may be enhanced by pressing an antenna onto the ICsuch that one or more “dimples” formed on the antenna make directcontact with one or more of the large contact pads on the IC. In someembodiments, the dimples are instead formed on the large contact pads.In some embodiment the dimples break through the nonconductive coveringmaterial. In other embodiments, galvanic coupling may be accomplishedwithout dimples or bumps, such as by direct contact or by means of anetchant to remove the nonconductive covering material.

Large contact pads 808/810 may cover a significant portion of the topsurface of IC 802. For example, large contact pads 808/810 may covermore than 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or even up to 100% ofthe top surface of IC 802. Regardless of the amount of coverage, largecontact pads 808/810 are distinguishable from bumps by theirpredisposition to have at least one of (1) a surface area that is asignificant fraction of the size of underlying IC 802, (2) a surfacearea that is many times larger than that of underlying IC contacts 633,(3) a low aspect ratio (height versus width or height versus surfacearea), and/or (4) a flat or textured-flat top. By contrast, bumpstypically have (1) a surface area that is small relative to the size ofunderlying IC 802, (2) a surface area that is similar or perhaps twicethat of underlying IC contacts 633, (3) a high aspect ratio (heightversus width or height versus surface area), and (4) a rounded top. Inaddition, large contact pads 808/810 tend to have an as-designed shape,whereas bumps tend to assume a shape similar that of their underlying ICcontacts (i.e. circular-looking if the underlying bumps are circular oroctagonal-looking if the underlying IC contacts are octagonal). Ofcourse, not all of these differences are required or absolute, but alarge contact pad is easily distinguishable from a bump by one ofordinary skill in the art.

In some embodiments, the combined area of all contact pads on aparticular surface of the IC does not exceed the area of that particularsurface, and any contact pads on a surface of an IC are confined withinor extend up to that surface's perimeter. In other embodiments, largecontact pads may extend out beyond the perimeter of an IC surface andmay wrap around or encroach onto neighboring IC surfaces, or even extendoutward from the IC surface in a cantilevered fashion.

Whereas large contact pads 808/810 in diagram 800 are shown assubstantially rectangular, large contact pads do not need to berectangular. Large contact pads may be circular, annular, or may bedesigned to have any suitable shape. Diagram 850 depicts a top view ofIC 852 with one IC contact pair having contacts 854 a and 854 b (similarto contacts 804 a and 804 b) and another IC contact pair having contacts856 a, 856 b (similar to contacts 806 a and 806 b). Large contact pads858 and 860 overlie and electrically couple to IC contacts 854 a and 856a, respectively. IC contact pads 854 b and 856 b may remain electricallyisolated, may couple to other electrical elements, may have any otherpurpose, or may not even exist.

Large contact pads 858 and 860 may be fabricated and shaped bypatterning a conductive redistribution layer as described above inreference to FIG. 6 . The shapes and/or orientations of the contactareas may be based on aesthetics, ease of electrically coupling toantenna terminals, ease of etching or forming, utility as an etch-stopin an etching step, reducing parasitic coupling to sensitive componentsin IC 802/852, or for any other reason. In some embodiments largecontact pads may be patterned so that regions whose local parasiticcapacitance to IC 802/852 (or elements in IC 802/852) would exceed athreshold are excised. The portions may be removed after deposition ornot deposited in the first place. The threshold(s) may be determinedbased on, for example, a desired parasitic capacitance of the entire ICor a desired local parasitic capacitance of a portion of the IC. Also asshown in diagram 850, contact areas 808 and 810 may have curved orrounded edges, for example to ease masking, etching, and/or liftoffpatterning processes.

In some embodiments, the surface area of a conductive redistributionlayer (e.g., redistribution layer 634) or a large contact pad fashionedfrom such a redistribution layer (e.g., contact pad 808) that isavailable for electrical coupling to an antenna may be much larger thanthe surface area of the interface between the redistribution layer andthe IC contact (e.g., IC contacts 633 or contact 804 a). For example,the surface area of large contact pad 808 is shown to be substantiallylarger than the total surface area of the interface between largecontact pad 808 and IC contacts 804 a and 804 b. Likewise, the surfacearea of large contact pad 810 is shown to be substantially larger thanthe total surface area of the interface between large contact pad 810and IC contacts 806 a and 806 b. In some embodiments, the surface areaof a large contact pad available for electrical coupling to an antennamay be at least three times (300%), five times (500%), ten times(1000%), or even twenty times (2000%) or more larger than the surfacearea of the interface between the large contact pad and one or more ICcontacts.

In some embodiments, a contact location between a contact layer andantenna terminal may differ from a contact location between the contactlayer and the IC. Such offset and nonoverlapping connections may provideflexibility in terms of the placement of the IC onto the antennaterminals. FIG. 9 depicts nonoverlapping or offset contacts according toembodiments, and depicts a top view 900 and a cutaway view 950 (takenalong the A-A′ axis shown in view 900). In FIG. 9 , an IC 902 has ICcontacts 904 and 906. A repassivation layer 920 is disposed over the ICcontacts 904 and 906, and contact pads 908 and 910 are disposed on therepassivation layer 920. The contact pads 908 and 910 may be formed bypatterning a deposited contact layer. The IC contacts 904 and 906 areelectrically connected through the repassivation layer 920 to thecontact pads 908 and 910, respectively. As shown in view 950, IC contact906 may be electrically connected to contact pad 910 via a bump 922(similar to bump(s) 632) formed through an opening in the repassivationlayer 920. A similar bump (not shown) may electrically connect ICcontact 904 to contact pad 908 through another opening in therepassivation layer 920. In some embodiments, the contact pads 910 and908 may directly electrically connect with the IC contacts 906 and 904,respectively, without bumps. For example, the contact pads 910/908 maybe deposited on an opening in the repassivation layer 920, directlyforming an electrical connection with underlying IC contacts 906/904.

The contact pads 908 and 910 are further electrically connected toantenna terminals 912 and 914, respectively. In particular, contact pad908 electrically connects to antenna terminal 912 through contact area916, and contact pad 910 electrically connects to antenna terminal 914through contact area 918. If an oxide, masking, or other nonconductivelayer covers the contact pads and/or the antenna terminals, openings maybe formed at the contact areas 916 and 918 before the electricalconnections are made, as described above.

While FIG. 9 depicts connections/openings that are entirely offset andnonoverlapping, in other embodiments the connections/openings maypartially overlap, or a connection (e.g., a contact pad/antenna terminalconnection) may wholly encompass another connection (e.g., a contactpad/IC contact connection).

Large IC contact pads as described herein may also assist in thepositioning of an IC on a substrate. FIG. 10 illustrates a top view 1000and a side view 1050 of a tag self-assembly method according toembodiments. In FIG. 10 , an IC 1002 is to be deposited on a substratehaving antenna terminals 1008 and 1010. In particular, IC 1002 is to bedeposited such that first IC contact pad 1004 overlaps first antennaterminal 1008 (but not second antenna terminal 1010) and second ICcontact pad 1006 overlaps second antenna terminal 1010 (but not firstantenna terminal 1008).

Liquid surface tension may be used to facilitate the alignment of eachcontact pad with its respective antenna terminal. Surface tensionresults from cohesive forces between liquid molecules. When two dropletsof similar liquid (or liquids having similar surface energies) areplaced close to each other, they will tend to coalesce into a single,larger droplet in order to minimize the number of exposed molecules andthereby minimize surface energy. If the two droplets are each associatedwith a different object, the coalescence of the two droplets may alsopull the different objects together.

In FIG. 10 , at least some of the contact pads and/or the antennaterminals may each be associated with a liquid droplet. For example,contact pad 1004 may be associated with droplet 1012, contact pad 1006may be associated with droplet 1014, antenna terminal 1008 may beassociated with droplet 1016, and antenna terminal 1010 may beassociated with droplet 1018. When IC 1002 is brought into closeproximity to the substrate (and antenna terminals 1008 and 1010),droplet 1012 may be attracted to droplet 1016, thus drawing IC pad 1004into contact with antenna terminal 1008. Similarly, droplet 1014 may beattracted to droplet 1018, drawing IC pad 1006 into contact with antennaterminal 1010.

In one embodiment, the liquid droplets 1012-1018 may include water. Insome embodiments, the liquid droplets may also include one or moreliquid adhesives, such as a conductive, nonconductive, oranisotropically conductive adhesive. Liquid droplets 1012-1018 mayresult from solid material. For example, a solid film or solid particlesmay first be deposited on the contact pads and/or the antenna terminals.The deposited solid material may then be heated, chemically modified, orotherwise processed to form the liquid droplets 1012-1018. For example,solid solder may initially be deposited on the contact pads and/or theantenna terminals. Just prior to the assembly process, heat may beapplied to IC 1002 and/or the substrate (for example, using impulseheating as described below) in order to melt the solid solder intoliquid solder droplets. Subsequently, IC 1002 may be brought into closeproximity to the substrate (and antenna terminals 1008 and 1010), andthe liquid solder droplets on the IC contact pads and/or the antennaterminals may coalesce to draw the IC and the substrate together. Insome embodiments, IC 1002 may be brought into close proximity to thesubstrate before heat is applied. Subsequently, heat may be applied(e.g., using impulse heating as described below) to melt the solidsolder deposited on the contact pads and/or the antenna terminals, whichcauses contact pads and antenna terminals close to each other to bedrawn together (via droplet coalescence). Of course, solid materialsother than solder may be used.

In some embodiments, different types of liquids may be used for eachpair of IC pad and antenna terminal. For example, a first type of liquidmay be placed on IC pad 1004 and antenna terminal 1008, and a secondtype of liquid may be placed on IC pad 1006 and antenna terminal 1010.The liquid types may be selected to have different surface tensionproperties, such that droplets of the first type of liquid do notattract droplets of the second type of liquid. For example, droplets ofa polar liquid (e.g., water) may be placed on IC pad 1004 and antennaterminal 1008, and droplets of a nonpolar liquid (e.g., an oil) may beplaced on IC pad 1006 and antenna terminal 1008. In some embodiments,substances that are liquid under different conditions may be used. Forexample, water droplets may be placed on IC pad 1004 and antennaterminal 1008, and solid solder may be placed on IC pad 1006 and antennaterminal 1010. When the IC is initially deposited on the substrate, ICpad 1004 and antenna terminal 1008 will be drawn together by theirassociated water droplets. Subsequently, the IC and substrate may beheated such that the solid solder on IC pad 1006 and antenna terminal1010 melt and draw the pad and terminal together.

While FIG. 10 depicts liquid droplets on each of the IC pads and antennaterminals, in some embodiments liquid droplets may be present on onlyone IC pad or antenna terminal in each pair of IC pads and antennaterminals. In these embodiments, the liquid droplet on the IC pad (orantenna terminal) may be preferentially attracted to the material of theantenna terminal (or IC pad). For example, a droplet of a polar liquid(e.g., water) may be preferentially attracted to a metal (e.g., themetal of an IC pad or antenna terminal).

Other techniques may also be used to assemble or align ICs onto antennaterminals on a substrate. As one example, electrostatic attraction maybe used to assemble an electrically-charged IC onto oppositely-chargedantenna terminals. The charge on the IC and/or antenna terminals may beinduced by a laser (e.g., as with laser printing) or by any othersuitable means.

As described above, an IC may be galvanically or conductively connectedto the conductive trace of an antenna by, for example, using a dimple orbump on the trace to directly connect the trace to a large contact padon the IC. In some embodiments, an IC contact pad may be galvanicallyconnected to an antenna without the use of a dimple, bump, or raisedregion.

FIGS. 11A and 11B illustrate tag precursors having ICs galvanicallyconnected to antenna terminals on tag substrates according toembodiments. A tag precursor is a portion of a complete RFID tag, andincludes the RFID IC and either a substrate having the entire tagantenna (i.e., an inlay) or a substrate having only a portion of theentire tag antenna (i.e., a strap). In the latter case, the strap maythen be attached to an inlay.

FIG. 11A depicts an IC 1102 and a tag substrate 1108. IC 1102 includesone or more large contact pads 1104 that electrically connect to one ormore electrical circuit elements within IC 1102. Tag substrate 1108,which may be a strap or an inlay, includes an antenna terminal 1110,which may be a trace of metal similar to antenna traces 320 and 322described in FIG. 3 . If antenna terminal 1110 includes an oxidizingmetal such as aluminum or copper, an oxide layer 1112 may form onterminal 1110, for example due to exposure to air. Oxide layer 1112, ifallowed to remain, acts as an insulating layer which prevents theformation of a galvanic connection between IC pad 1104 and antennaterminal 1110.

To address this issue, an additional layer 1106 may be added tofacilitate the formation of a galvanic connection between IC pad 1104and antenna terminal 1110. In some embodiments, additional layer 1106includes etchants for forming openings by etching or breaking throughoxide layer 1112. For example, additional layer 1106 may includeparticles (spherical, ovoid, angular, sharp-edged, etc.) that formopenings in the oxide layer 1112 by rupturing it when heat and/orpressure are applied. In one embodiment, particles suspended in afast-drying binder or liquid may be applied to the IC 1102 or thesubstrate 1108 and then dried to form the additional layer 1106.

Additional layer 1106 may also (or instead) include substance(s) foretching or reacting with oxide layer 1112 to form openings. In someembodiments, such substances may include compounds for chemicallyreducing oxides (i.e., decreasing the oxidation state of anoxygen-containing compound by adding electrons to the compound), such assolder flux or any other suitable acidic compound or substance. Theparticular substances used may be selected based on the material to beetched/reacted with. For example, if antenna terminal 1110 includesaluminum, additional layer 1106 may include an etchant or reducingsubstance for aluminum oxide. When IC 1102 with additional layer 1106 isdisposed on antenna terminal 1110, components in additional layer 1106(e.g., the particles and/or substances described above) create openingsin oxide layer 1112, thus allowing IC pad 1104 to form a galvanicconnection with antenna terminal 1110. In some embodiments, heat and/orpressure may be applied to additional layer 1106 to facilitate thecreation of openings in oxide layer 1112 and the formation of galvanicconnections between IC pad 1104 and antenna terminal 1110. For example,applying heat to an etchant, reactant, or reducing substance mayaccelerate the oxide etch/reaction/reduction process.

In some embodiments, the additional layer 1106 may include an adhesivefor attaching the IC 1102 to the tag substrate 1108. For example, theadhesive may include an isotropic or anisotropic conductive materialand/or a nonconductive adhesive. In some embodiments, the adhesive mayalso include one or more of the mechanical and/or chemical etchants orreactants described herein (e.g., particles, etchants, reducingsubstances, solubilizing substances, dopants, etc.), while in otherembodiments the adhesive may be separate from the etchant(s).

If the additional layer 1106 is electrically conductive, the galvanicconnection between IC pad 1104 and antenna terminal 1110 may be formedthrough the additional layer 1106. For example, if the additional layer1106 includes conductive particles for forming openings in the oxidelayer 1112, the conductive particles may help form the galvanicconnection. If the additional layer 1106 is not electrically conductive,it may be removed as a result of applied heat, pressure, or otherprocessing, thus allowing IC pad 1104 to directly contact antennaterminal 1110 to form a galvanic connection (e.g., after applyingpressure, heat, or some other processing). In some embodiments, the ICpad 1104 itself may have a textured surface (e.g., surfaceirregularities, ridges, protrusions, and/or other topological features)for etching or rupturing oxide layer 1112 when heat and/or pressure isapplied. For example, the IC pad 1104 may be fabricated to includerelatively sharp-edged ridges or bumps on its surface in a patterned orrandom arrangement. In some embodiments, laser-assisted etching or othermethods of selective etching may be used to provide surface texturing onthe IC pad 1104.

FIG. 11B depicts a diagram 1150 similar to diagram 1100 in FIG. 11A.However, instead of an oxide layer, a masking layer 1152 covers antennaterminal 1110. Masking layer 1152 may be deposited after antennaterminal 1110 is formed to serve as a protective layer that prevents theformation of an oxide layer on the antenna terminal. The masking layer1152 may include an organic or inorganic dielectric material, or mayeven include a metallic or other electrically-conductive material thatpreferably does not oxidize. If masking layer 1152 includes a dielectricor insulating material, additional layer 1106 may include substance(s)for reacting with, etching, reducing, or solubilizing masking layer 1152and/or particles that rupture masking layer 1152 when heat and/orpressure is applied. If masking layer 1152 includes anelectrically-conductive material, additional layer 1106 may includematerial for galvanically connecting IC pad 1104 and masking layer 1152,or may not even be present.

While heat and/or pressure applied to an IC or a tag substrate may beused to accelerate the formation of openings in an oxide or maskinglayer and/or form a galvanic connection (e.g., as described previously),in some embodiments processing other than heat and/or pressure may alsobe used. For example, an electric field may be applied between IC pad1104 and antenna terminal 1110. The electric field may facilitateetching of any oxide layer (e.g., oxide layer 1112) by, for example,increasing the etching rate and/or the etching selectivity. The electricfield may also facilitate the physical formation of the galvanicconnection between IC pad 1104 and antenna terminal 1110 by, forexample, electronically welding the pad to the terminal or promotingelectromigration of metallic ions such that pad 1104 is electricallyshorted to terminal 1110. As another example, ultrasonic welding may beused to disrupt oxide layer 1112 and/or electrically short pad 1104 toterminal 1110.

In some embodiments, reactants or substances in the additional layer1106 may react with the oxide layer 1112 or the masking layer 1152 toform a conductive pathway between IC pad 1104 and antenna terminal 1110without having to form openings in the oxide layer 1112 or the maskinglayer 1152. For example, the masking layer 1152 may include anonconductive plastic. When the additional layer 1106 is in contact withthe masking layer 1152, dopants in the layer 1106 may diffuse intoportions of the masking layer 1152, turning those portions conductiveand creating the conductive pathway. In some embodiments, heat and/orpressure may be used to facilitate the diffusion/reaction.

In some embodiments, low-melting-point metals (e.g., solder as describedabove) or metal precursors may be used to form electrical connectionsbetween IC contacts and substrate terminals/contacts. A “metalprecursor” is a material that can be processed to formelectrically-conductive structures electrically coupling two contacts orterminals. Processing of a metal precursor includes the application ofheat and/or pressure to the metal precursor to at least partially melt,sinter, or otherwise cause the metal precursor to become an electricallyconductive structure. In some embodiments, a metal precursor may beprocessed to form a physical bond between two other electricallyconductive structures (e.g., an IC contact and a substrateterminal/contact).

Metal precursors may be electrically conductive before processing, ormay be insulating before processing and electrically conductive afterprocessing. For example, a metal precursor that is electricallyconductive before processing may include metal particles or a thin layerof metal without a nonconductive coating (e.g., an oxide). A metalprecursor that is electrically conductive after processing may includemetal particles or layers coated with a nonconductive material, such asan oxide or other insulating layer, particles formed of metal oxides,metal particles in a nonconductive matrix or carrier, or any othermetal-containing compound or material that is relativelyelectrically-insulating before processing and electrically conductiveafter processing. Metal precursors may be a thin layer of metal ormetallic particles, solder powder, or solder paste, and may includealuminum, tin, palladium, copper, silver, gold, bismuth, any combinationof the previous, or any other suitable metal. In some embodiments, metalprecursors may include a chemical etchant, reducing substance, orsolubilizing substance for etching or reacting with oxides or maskinglayers, as described above in FIG. 11 .

In some embodiments a metal precursor may only be metallic in the senseof being electrically conductive after processing, and may not include ametal at all. For example, a metal precursor may include a nonmetallicorganic or inorganic layer that becomes electrically conductive afterthe application of heat and/or pressure. Regardless of whether a metalprecursor actually includes metal or not, in some embodiments thematerials in the metal precursor may be capable of forming anelectrically-conductive structure upon processing with relatively lowheat or pressure. For example, the metal precursor may include one ormore low-melting-point metals.

FIG. 12 depicts the deposition of metal precursors on RFID integratedcircuits according to embodiments. Diagram 1200 depicts an RFID IC 1202with an insulating layer 1206 and IC contacts 1204 (similar to ICcontacts 432 and 433) electrically connected to circuitry within the IC1202. Structures 1208 (e.g., bumps) are formed of metal precursors asdescribed above, and may be deposited onto the IC 1202 so as tophysically contact IC contacts 1204. In some embodiments, structures1208 may be partially processed after deposition to physically attachand electrically couple to IC contacts 1204. Upon further physicalcontact with different contacts (e.g., antenna terminals) and subsequentprocessing, as described below in FIG. 13 , structures 1208 may becomeelectrically conductive, thereby electrically coupling IC contacts 1204to the other contacts or terminals.

Diagram 1220 depicts a similar RFID IC 1202. However, spacers 1222physically separate structures 1208 from IC contacts 1204. In someembodiments, spacers 1222 may include a conductive material, such as ametal (e.g., copper, aluminum, palladium, gold, or any other suitablemetal), and may electrically couple structures 1208 to IC contacts 1204.In some embodiments, structures 1208 may be partially processed afterdeposition to physically attach and electrically couple to spacers 1222.

Diagram 1240 depicts structures being deposited via a powder-coatingprocess. The RFID IC 1202, similar to the ICs described above, may beelectrostatically charged. Electrostatically charged metal precursorparticles 1242 may then be applied to the IC 1202. If the polarity ofthe charge on the particles 1242 opposes the polarity of the charge onthe IC 1202, then the particles 1242 will be attracted to and adhere tothe IC 1202. In some embodiments, the particles 1242 preferentiallyadhere to the IC contacts 1204 and avoid the insulating layer 1206.After the particles 1242 are applied to IC 1202, the particles 1242 maybe partially processed to cause them to attach and electrically coupleto the IC contacts 1204. Subsequently, the partially-processed particles1242 may be brought into physical contact with other contacts and fullyprocessed to electrically couple IC contacts 1204 with the othercontacts, as described above in diagram 1200.

Structures 1208 and particles 1242 may be deposited onto IC contacts1204 or spacers 1222 in any number of ways. For example, metalprecursors may be deposited to form structures 1208 using amasked-coating process, a silk-screening process, a vapor depositionprocess, an evaporation process, and/or a sputtering process. In someembodiments, the metal precursor may be deposited on IC contacts 1204during the fabrication of IC 1202 to serve as an oxidation barrier forIC contacts 1204, thereby preventing oxidation of IC contacts 1204.Particles 1242 may be deposited using a powder-coating process (asdescribed above), a masked-coating process, or a silk-screening process.

While metal precursors are described above as being deposited or appliedonto ICs, metal precursors may also (or instead) be applied to contactson an inlay or strap substrate in similar fashion. For example, metalprecursors may be deposited using any of the techniques described aboveonto antenna terminals or strap contacts on a substrate, and thensubsequently partially-processed to attach and electrically couple tothe substrate terminals/contacts. In some embodiments, antenna terminalsor strap contacts on a substrate may be formed using metal precursors.For example, an antenna-terminal precursor (which may include metalprecursors) may be deposited on a substrate at a location where anantenna terminal is desired. Similar to a metal precursor, theantenna-terminal precursor may be capable of forming anelectrically-conductive structure upon processing with relatively lowheat or pressure, and may be electrically conductive before processing,or may be insulating before processing and electrically conductive afterprocessing. In some embodiments the antenna-terminal precursor may notinclude any metals, and may instead include a nonmetallic organic orinorganic layer that becomes electrically conductive after theapplication of heat and/or pressure.

The deposited antenna-terminal precursor may then be processed to form aconductive antenna terminal. In some embodiments, an IC may first beplaced such that an IC contact physically contacts the antenna-terminalprecursor, and the antenna-terminal precursor may then be subsequentlyprocessed to form both a conductive antenna terminal and a physicalbond/electrical connection between the antenna terminal and the ICcontact.

As described above, metal precursors may be processed using heat and/orpressure to form metallic or electrically-conductive structures thatphysically bond to IC contacts (e.g., IC contacts 1204) and antennaterminals. In some embodiments, impulse heating is used to apply heat tometal precursors. Impulse heating refers to a localized heating processwhere a controlled amount of thermal energy is delivered to a specifictarget location over a specific time duration, and may be useful becausesignificant amounts of thermal energy can be delivered to specificlocations without excessive heating of the surrounding environment,thereby reducing the possibility of environmental damage. For example,if a tag inlay or strap includes an organic polymer, such aspolyethylene terephthalate (PET), impulse heating may be used to processmetal precursors on the inlay without melting, damaging, or otherwisedegrading the organic polymer.

The amount of thermal energy delivered by an impulse heating process maybe determined based on the desired effect. For example, when impulseheating is used to process a metal precursor structure such as structure1208, the amount of thermal energy to be delivered may be determinedbased on the material characteristics of the metal precursor (e.g., heatcapacity and/or melting point), size of the metal precursor (dimensions,volume, and/or mass), desired outcome (e.g., partial melting orsintering of the metal precursor), anticipated losses in delivery (e.g.,losses incurred from passing through a medium and/or from dissipation atthe target location), and/or material characteristics of the surroundingenvironment (e.g., the melting point or temperature tolerance of thesubstrate or IC components).

The target location for the impulse heating process may be determinedbased on the structure to be processed. For example, when a laser isused for impulse heating of a metal precursor structure, the structureitself may serve as the target location, and the spot size of the lasermay be determined based on the amount of thermal energy to be delivered,the time duration of the delivery (as described below), the interveningmedium, the material characteristics of the surrounding environment,and/or the structure's size and heat propagation characteristics.

The time duration over which the impulse heating process deliversthermal energy may be determined based on the material of the metalprecursor, characteristics of the metal precursor structure,characteristics of the environment surrounding the structure, and/orcharacteristics of the intervening medium. For example, the timeduration may be selected such that the metal precursor structure reachesa first temperature (e.g., over the melting point or sinteringtemperature of the metal precursor), but does not exceed a secondtemperature (e.g., a temperature that would damage the environmentsurrounding the structure). The time duration may be selected to berelatively short, less than a second and on the order of milliseconds,to allow for rapid processing.

FIG. 13 depicts the assembly of RFID ICs to form inlays or straps usingimpulse heating of metal precursors according to embodiments. Apparatus1302 is configured to present inlay or strap substrates for ICplacement. Apparatus 1302 includes cylindrical drums or rollers thatdispense and gather a flexible backing or web, on which the substratesare mounted. ICs 1304 are mounted on a stretch frame 1306, which allowsa place tool 1308 to select an individual IC 1304 for assembly onto asubstrate. For example, place tool 1308 may press the back of stretchframe 1306 to bring an IC into physical contact with a substrate, asshown in FIG. 13 .

Diagram 1300 depicts a laser-based method for assembling ICs into inlaysor straps. The ICs 1304 and/or the substrates may have metal precursorstructures, as described above in FIG. 12 . When place tool 1308 causesan IC to physically contact a substrate, a laser 1310 may impulse-heatthe metal precursor structures by applying heat to the substrate and/orthe IC as described above, processing the metal precursor structuresinto metallic, electrically-conductive structures that electricallycouple the IC to antenna terminals or strap contacts on the substrate.

The ICs and/or the substrates may be impulse-heated using other methods.Diagram 1320 depicts an infrared-based method for assembling ICs ontoinlays. Diagram 1320 is similar to diagram 1300, but uses an infraredlight source 1322 to perform the impulse-heating instead of a laser.Similarly, diagram 1340 depicts a method using a thermode or heatingelement 1342 to perform the impulse-heating.

FIG. 14 is a flowchart depicting a process 1400 for assembling RFID ICsonto inlays using impulse heating of metal precursors according toembodiments. In step 1402, RFID integrated circuits (ICs) arefabricated. IC fabrication includes the formation of IC contacts (e.g.,IC contacts 1204 in FIG. 12 ) and the deposition of insulating layers(e.g., insulating layer 1206 in FIG. 12 ). The IC fabrication step mayalso include the deposition of spacers such as spacers 1222 in FIG. 12 .In some embodiments, metal precursor layers may also be deposited on ICcontacts in step 1402, for example to serve as an oxidation barrier forthe IC contacts.

In step 1404, metal precursor structures (e.g., structures 1208 in FIG.12 ) are deposited onto the fabricated ICs and/or substrates onto whichthe ICs are to be assembled. The metal precursor structures may bedeposited using any suitable method, such as powder-coating,masked-coating, silk-screening, vapor deposition, evaporation, orsputtering, as described above. If oxides or masking layers are presenton the contacts of the ICs and/or antenna terminals on the substrate, asubstance that etches, reacts with, or reduces the oxides/masking layers(as described above) may be deposited along with or in addition to themetal precursor structures. For example, the substance may be depositedto cover the metal precursor structures, or may be incorporated into themetal precursor structures. In some embodiments, the metal precursorstructures may take the place of antenna terminals on the substrate (asdescribed above) and/or IC contacts.

In step 1406, the IC is placed onto or otherwise brought into contactwith the substrate, as described in FIG. 13 . Finally, in step 1408 theIC, the substrate, and/or the metal precursor structures may beimpulse-heated as described in FIG. 13 to process the metal precursorstructures into metallic conductors electrically coupling the IC toterminals or contacts on the substrate. In embodiments where oxides ormasking layers are present and the metal precursor structures include asubstance to chemically remove the oxides/masking layers, the impulseheating may heat the substance to accelerate the oxide/masking layerremoval process.

The steps described in process 1400 are for illustration purposes only.RFID IC assembly onto substrates using impulse-heating of metalprecursors may be performed employing additional or fewer steps and indifferent orders using the principles described herein. Of course theorder of the steps may be modified, some steps eliminated, or othersteps added according to other embodiments.

ICs as described herein may also be configured and/or implementfunctionalities as described in Patent Cooperation Treaty (PCT)Application PCT/US12/54531 filed on Sep. 10, 2012 and U.S. patentapplication Ser. No. 14/132,959 filed on Dec. 18, 2013. The disclosuresof the aforementioned applications are hereby incorporated by referencefor all purposes.

Embodiments also include methods of assembling a tag as describedherein. An economy is achieved in the present document in that a singledescription is sometimes given for both methods according toembodiments, and functionalities of devices made according toembodiments.

Embodiments may be implemented using programs executed by fully orpartially automated tag manufacturing equipment. A program is generallydefined as a group of steps or operations leading to a desired result,due to the nature of the elements in the steps and their sequence. Aprogram is usually advantageously implemented as a sequence of steps oroperations for a processor, such as the structures described above.

Performing the steps, instructions, or operations of a program requiresmanipulation of physical quantities. Usually, though not necessarily,these quantities may be transferred, combined, compared, and otherwisemanipulated or processed according to the steps or instructions, andthey may also be stored in a computer-readable medium. These quantitiesinclude, for example, electrical, magnetic, and electromagnetic chargesor particles, states of matter and in the more general case can includethe states of any physical devices or elements.

Embodiments may furthermore include storage media for storing theprograms discussed above. A storage medium according to the embodimentsis a machine-readable medium, such as a memory, and is read by aprocessor controlling a tag assembly machine for assembling tagsaccording to embodiments. If a memory, it can be implemented in a numberof ways, such as Read Only Memory (ROM), Random Access Memory (RAM),etc., some of which are volatile and some non-volatile.

The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theembodiments. Although the subject matter has been described in languagespecific to structural features and/or methodological acts, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims and embodiments.

We claim:
 1. A method for assembling a Radio Frequency Identification(RFID) tag precursor, the method comprising: providing an assemblyincluding an RFID integrated circuit (IC), a nonconductive repassivationlayer on a surface of the IC and confined within a perimeter of thesurface, and a conductive redistribution layer on the repassivationlayer and confined within the perimeter of the surface, in which atleast a portion of the redistribution layer is electrically connected tothe IC through an opening in the repassivation layer; providing asubstrate including an antenna-terminal precursor; disposing theassembly onto the substrate such that the portion of the redistributionlayer physically contacts the antenna-terminal precursor; and impulseheating the antenna-terminal precursor to form both an antenna terminaland an electrical connection to the portion of the redistribution layer,wherein the electrical connection and the opening are at least partiallynonoverlapping.
 2. The method of claim 1, wherein the antenna-terminalprecursor includes a reducing substance and impulse heating theantenna-terminal precursor comprises heating the reducing substance toaccelerate the reduction of an oxide on the portion of theredistribution layer.
 3. The method of claim 1, wherein impulse heatingthe antenna-terminal precursor comprises forming a physical bond betweenthe antenna terminal and the portion of the redistribution layer.
 4. Themethod of claim 1, wherein the electrical connection and the opening areentirely nonoverlapping.
 5. The method of claim 1, wherein theantenna-terminal precursor includes at least one of solder powder,solder paste, unsintered metal, and a thin metal layer, and includes atleast one of tin, palladium, copper, silver, or bismuth.
 6. The methodof claim 1, wherein the impulse heating uses at least one of a laser, aninfrared light source, or a thermode.
 7. A Radio FrequencyIdentification (RFID) tag precursor comprising: an assembly including anRFID integrated circuit (IC), a nonconductive repassivation layer on asurface of the IC, and a conductive redistribution layer on therepassivation layer, in which at least a portion of the redistributionlayer is electrically connected to the IC and; a substrate including anantenna-terminal precursor physically contacting the portion of theredistribution layer, wherein: the antenna-terminal precursor is impulseheated to form both an antenna terminal and a metallic conductor formingan electrical connection between the portion of the redistribution layerand the antenna terminal.
 8. The tag precursor of claim 7, wherein: theantenna-terminal precursor includes a reducing substance; theredistribution layer has an oxide layer; the impulse heating heats thereducing substance to accelerate the reduction of the oxide layer,thereby forming at least one opening in the oxide layer; and themetallic conductor forms the electrical connection through the at leastone opening in the oxide layer.
 9. The tag precursor of claim 8, whereinthe antenna-terminal precursor includes at least one of solder powder,solder paste, unsintered metal, and a thin metal layer, and includes atleast one of tin, palladium, copper, silver, or bismuth.
 10. The tagprecursor of claim 7, wherein the impulse heating uses at least one of alaser, an infrared light source, or a thermode.
 11. The tag precursor ofclaim 7, wherein an electrical connection between the portion of theredistribution layer and the IC is at least one of through an opening inthe repassivation layer or through a side contact.
 12. The tag precursorof claim 11, wherein the opening and the electrical connection betweenthe portion of the redistribution layer and the antenna terminal are atleast partially nonoverlapping.
 13. The tag precursor of claim 7,wherein both the repassivation layer and the redistribution layer areconfined within a perimeter of the surface of the IC.
 14. A RadioFrequency Identification (RFID) strap comprising: an assembly includingan RFID integrated circuit (IC), a nonconductive repassivation layer ona surface of the IC and confined within a perimeter of the surface, anda conductive redistribution layer on the repassivation layer andconfined within the perimeter of the surface, in which at least aportion of the redistribution layer is electrically connected to the IC;and a substrate including a metal precursor physically contacting theportion of the redistribution layer, wherein: the metal precursor isimpulse heated to form both a strap contact configured to electricallycouple to an antenna and a metallic conductor forming an electricalconnection between the portion of the redistribution layer and the strapcontact.
 15. The strap of claim 14, wherein the metal precursor includesa reducing substance; at least one of the redistribution layer and theantenna has an oxide layer; the impulse heating heats the reducingsubstance to accelerate the reduction of the oxide layer, therebyforming at least one opening in the oxide layer; and the metallicconductor forms the electrical connection through the at least oneopening in the oxide layer.
 16. The strap of claim 14, wherein the metalprecursor includes at least one of solder powder, solder paste,unsintered metal, and a thin metal layer, and includes at least one oftin, palladium, copper, silver, or bismuth.
 17. The strap of claim 14,wherein the impulse heating uses at least one of a laser, an infraredlight source, or a thermode.
 18. The strap of claim 14, wherein anelectrical connection between the portion of the redistribution layerand the IC is at least one of through an opening in the repassivationlayer or through a side contact.
 19. The strap of claim 18, wherein theopening and the electrical connection between the portion of theredistribution layer and the strap contact are at least partiallynonoverlapping.
 20. The strap of claim 14, wherein the repassivationlayer and the redistribution layer are both confined within a perimeterof the surface of the IC.